The human body is equipped with a defense system called immunity. When a foreign substance such as bacterium or virus (antigen) enters the body, a protein called antibody is produced and attacks the antigen to protect the living body. Antibody medicine is a medicine using this effect of antibody. As the mechanisms of action of antibody medicine, activities such as antibody-dependent cell-mediated cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), neutralizing activity or apoptosis induction activity have been reported to be important. In particular, it has been reported that Fc receptor-mediated ADCC activity is the most important antitumor mechanism in Herceptin (therapeutic for metastatic breast cancer) and Rituxan (therapeutic for non-Hodgkin's lymphoma) (Non-Patent Document 1).
The effect of ADCC injures a target cell through the binding of an antibody to an antigen expressed on the target cell and the binding of the Fc portion of the antibody to an Fc receptor expressed on an effecter cell. Two binding activities, i.e., antigen-antibody binding activity and Fc/Fc receptor binding activity, are believed to be necessary for the manifestation of the effect of ADCC. Although antigen-antibody binding activity can be conventionally evaluated by competitive ELISA (cELISA) (Non-Patent Document 2) (FIG. 1), no method has been known to measure Fc/Fc receptor binding activity, to say nothing of a method to evaluate the above-mentioned two binding activities simultaneously.
Non-Patent Document 1: Clybes, R. A., et al., 2000. Inhibitory Fc receptors modulate in vivo cytoxicity against tumor targets. Natl. Med. 6: 443
Non-Patent Document 2: Human monoclonal antibody stability and activity at vaginal pH, Journal of Reproductive Immunology 56, 61-76 (2001)